1. Field of the Invention
The present invention relates to positioning, such as through rotation and/or translation, using electromagnetic interactions.
2. Background Art
That certain “stones” would attract bits of iron has been well known for centuries. Such materials that have such metal attracting properties are called magnets. A magnet is said to have what is known as magnetic lines of force, invisible to the naked eye but measurable none the less. These lines of force radiate from each end of a bar magnet. Each end is said to be polarized, one being a north (N) pole and the other a south (S) pole. The strength of this magnetic field is dependent on the strength of the magnet. This type of magnet is sometimes called a permanent magnet.
In 1820 Oersted discovered that a current in a wire can also produce magnetic effects, namely, that such current could change the orientation of a compass needle. The magnetic effect of the current through a wire can be intensified by forming the wire into a coil with many turns. The space around the magnet or current carrying wire is defined as the site of a magnetic field. The magnetic effect of current flowing through a coil can be further intensified by providing an iron core inside the coil.
Magnetic actuators take advantage of magnetic effects. Magnetic actuators appear in many forms, including relays, motors, automatic valves, and the like. Magnetic actuation offers the possibility of generating repulsive forces in addition to attractive forces, increasing the flexibility of magnetic actuators.
Current controlled magnetic fields may be used for actuation or positioning of objects. One example is the stepper motor. A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. The shaft or spindle of a stepper motor rotates in discrete step increments when electrical command pulses are applied in the proper sequence. Motor rotation has several direct relationships to these applied input pulses. The sequence of the applied pulses is directly related to the direction of the motor shaft rotation. The speed of motor shaft rotation is related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied. One problem with stepper motors is that they provide only one-dimensional rotational positioning due to their cylindrical construction.
Another example is the linear motor. Linear motors use a plurality of coils on one flat surface and a plurality of magnets or coils on an interfacing flat surface. By appropriately energizing the coils, the first surface may be made to slide relative to the second surface. One problem with linear motors is that they provide only sliding motion between the two surfaces.
Many applications require complex motions, such as combinations of translation and rotation. These applications include aiming, such as for cameras, microphones, light sources, and the like. Other applications include positioning devices in space, such as robotic manipulators, probes, and the like. Still other applications include transporting systems such as conveyers, remotely controlled devices, robots, and the like. What is needed is to supply multiple degrees or types of motion with a single actuator.